Bright copper plating



United States Pa BRIGHT CGPPER PLATING Christian J. Wernlund, Niagara Falls, N. Y., assignor to E. I. du Pont de Nemours and Company, Wrlmmgton,

Del., a corporation of Delaware No Drawing. Application October 9, 1956 Serial No. 614,825

6 Claims. (Cl. 204-52) g./l. and, for silver, about 0.008l.62 g./l.

The present application is a continuation-in-part of my 'copending application Serial Number 352,268, filed Apr1l 30, 1953, now abandoned.

Inorganic selenium compounds such as the selenites and selenates have been employed heretofore in aqueous electroplating baths.

Thus Weiner, Alien Property Custodian Publication Serial Number 351,241, published ,May 18, 1943, shows these compounds in silver plating baths and intimates that they may be utilized in copper cyanide baths. Actual trial of selenites and selenates in the'latter baths has shown that they do have some bright- Ecopper cyanide baths any one of which may be employed as the basic bath of the invention. Preferably they are made up from potassium salts and contain, in aqueous solution:

Satlsiac- Preferred Component tory Range Range (0z./gal.) (oz./gal.)

Potassium hydroxide 1-10 1-8 Free potassium cyanide 0. 5-4 1-2 Copper cyanide 5-20 8-14 The free potassium cyanide is that measured by the Liebig silver nitrate titration.

The cheaper sodium compounds may be substituted in whole or in part for those of potassium. Since the potassium formulations permit higher rates of copper deposition and produce slightly brighter deposits, they are technologically preferred.

The inorganic selenium compounds employed as brightening additives in the invention are preferably oxygencontaining compounds such as selenous and selenic oxides and acids and the corresponding salts, e. g., sodium and potassium selenite and selenate. The compound utilized must, of course, be soluble to some extent in the bath and should introduce no interfering or deleterious ion.

The quantity of selenium added is not sharply critical and may vary within limits. Thus about 0.6l26.l2 g./l. of additive considered as metallic selenium is usable with about 0.612-3.00 g./l. preferred. The weight of compound chosen should yield this weight of metal, the cor- ICC responding weight of H SeO selenous acid, for example, being about l-10 g./l.

The form of the additive employed with the selenium is also not particularly critical. Thus about any compound form of the additive may be used that is compatible with the bath, i. e., is soluble in the bath and does not change important bath characteristics such as pH. Cadmium and silver are generally added as the cyanides, Cd(CN) and Ag(CN). Complex cyanides such as KAg(CN) and other compounds are also usable. Trivalent bismuth compounds such as Bi(C H O .7H O represent the form preferred for this metal.

The quantity of the second metal added varies to some extent with the metal. It is generally rathersmall, but variable within limits. Usable ranges are, for cadmium, about 0.0077.0 g./1., for bismuth, about 0.0020.05 Preferred ranges are 0.070-3.50, 0.0020.0l, and 0.0080.08 g./l., respectively. Typical compound weights are 0.01-10 g./l. for Cd(CN) 0.01-0.2 g./l. for Bi(C H O .7I-I O, and 0.012.0 for AgCN.

Each of the three metallic additives used simultaneously with selenuim has some brightening characteristics of its own within narrow current density ranges. The efiects produced by the respective combinations are, however, much greater than the separate effects. The combined additives may, therefore, properly be called synergistic in their application.

It will be understood that not all metals are synergistically cooperative with selenium in cyanide copper baths. Thus such elements as zinc, arsenic,scobalt and iron do not effect any improvements in the plating or the deposit when employed with selenium.

The baths of this invention may produce rough deposits unless precautions are taken thereagainst. Known anti-pitting agents are, therefore, preferably added to the bath. Agents like betaines, e. g., C-decyl betaine shown by the Holt U. S. Patent 2,255,057, are satisfactory. A preferred agent contains about 30% of trimethyl benzyl ammonium chloride and 12.5% of C-decyl betaine, the remainder being water, and is supplied to the extent of about 5 g./l. of bath.

The conditions necessary for plating from the baths of this invention are substantially those of conventional aqueous copper cyanide plating. Thus the temperature may vary between about 60 and 95 C. with about C. preferred. Agitation as by stirring may be used if desired. Choice of the material of the cathodes or workpieces is optional.

A particular advantage of this invention is that it produces bright copper plate over a wider range of current densities (amperes/ft. -a./s. f.) or, in some instances, brighter copper than a copper cyanide bath containing no additive or any one of the four metallic additives alone. In some embodiments, bright plate may be formed continuously in a range of about 10-60 a./s. f. or even more. The plating of irregular objects having projections and recesses is consequently greatly simplified.

There follow some examples intended to illustrate, but not to limit, the invention in more detail. In these examples all percentages are by weight.

Example I This example shows the effect of selenium and cadmium as joint plating additives.

(a) There was made up a conventional aqueous copper cyanide electroplating solution containing 14 oz./ gal. of cuprous cyanide, 2.0 cz./gal. of free sodium cyanide, 6.0 oz./gal. of potassium hydroxide and 1.5 oz./gal. of sodium carbonate. 5 g./l. of the preferred C-betaine anti-pitting compound noted above were also added.

This conventional solution was placed in a 1000 ml.

a as joint additives.

and 0.67 oz.'/ gal. of the "aqueous anti-pitting oscillating, cathode \Hullv cell,.atn alempcraturepi 893:2?

C. and a test run made to.,.determine the bright plating range. No bright plate was obtained at a current density above-about Iia./s:;f;" a Q (b) To a portion of the conventionalfbathiofi (taywas iii-(-11); iA brightt-platingii'ange' oftEli-5221s:f; wasob;

t'ainedQ.

' V 1A 'controlruniwithzl10:gi/l; in-rthel bath andain the manneri of: (d) gave :a very brightzplatingmangei of l6,-'"37 hazy; band; is very. 1 undesirable:'sinceaiti occhrs A about; in

V V thegcentcrt of theibri'ght plating rangetoftseleninmcalone,

' Partznf the bath of (li) 'c6ntai i1ingLhothtllLZ gi/LFDf Cd(CN) and 1 g./l. of selenou'siacidz sfiowed arsihgle very:brightzplating"rangeefrom 13. to 36 a$ZSLfi witlir. no hazy band.. i I

' Examle lz V "This-example shows the-use ofseleniiini and s'ilveras joint plating additives. g [The-basic sodium cyanidejbath of-*l= (a) gaye a very bright-"platingrange of l2'-35 "a./s. f. whenjcontaining v 1.0 g./l. of silver cyanide and 2.'0 g./l;- of selenous bid;

amateu 7 rained in, the, range 7 21-126 a./ S. The bismuth w en alkali metal "salts of saidi'aci'jds and a soluble compound of a metal taken from the'cla'ss' consisting of cadmium in an amount from; aboi-ItTOJIW dto,71'g';;/l., bismuth inan' amount from about. 0.00210 0.05 'g./l., and silver in auamount from about 0.008 to 1.62 g./l.

H 2. Afiagueous ,bath;for electrodepositing; bright copper containing copper cyanide; I about 0.6l2-t-3L00. gJl, j of selenium supp lied as a member of the tgroups consisting of the selenui m. onides ,7 selenous and. selenie., acids and the a lkalilnietalf saltd Of said acids, and"0.070-'3-.50' gl/l of dissolved cadmium.

Example 3 'This-'example shows theuse"ofiseleniiitiirtidi'bismilth l A potassium-based plating fbta'th. lWstibflfree potassium cyanide, 5 02.! gal. "offpotas'siuniliydr jr ide taining about 30%oftrimethylfbenzylfamnio I ride and (12.5%jof C-dcyl betaine, wlien tstedji'ri a "Hull cell, this -b'atli"alone' gave no bright plate, above 10 a,/s.'f." I Q I When-g0'.03 0"g/l, ofbismuthttrioxide and"2.0 'g" ll; iselenous acid {were employed together in ftlie pd of umcontaining bath, 'briglitplatevvasphtainedin the ranges 10-20 and 26+60 a./s.f. v Ha y streaked'plate@3965.

3. An aque ouslbath for eleetrodepositing bright copper v cyanide, about;0;6l23=00}g./l.sofuse:

containing copp leniurn supplied as" a member o f the group consisting of the, selenium oxides,,.selenous, and slen ic acids; ands-the aIKaIijnetaLsaItS jo frsaidgacidsgandr 0100240101 gg/nof dis- V '4. An ueQusQbatliQfQrQelectrodepositingbrightcopp er ontain ng. cbpilj f yi id bdl t L 2v3.00%g disc: l'enuim supplied,ass a memberof, ;me. group; consisting of the ,selenium. oxides} sielenojus} and? selenic acids and. the alkalitftutal salts'fof said acid'sgand 0.008 008 Ig /la of dissolved silver. V v V 7' I s.- Thebath or claimnltcontainingadditionallylan anti-.

pitting a t! is abetaine. 7 g

' 'nez'ae a derainedisarmament UNITED STATES-PATENTS;

2,732,336; Ostrdw a1i:24,'19s6' 2,737,485 (Dverc'a'shi-e al Mar;6, 1956 2-,770," 5s7 ostmw (Nov- 1331956 cIa-V'LtnE'S in the vant ii-pittingiagent' 

1. AN AQUEOUS BATH FOR ELECTRODEPOSITING BRIGHT COPPER CONTAINING COPPER CYANIDE A DUAL METALLIC BRIGHTENINGENING AGENT COMPRISING ABOUT 0.612-6.12 G./L. OF METALLIC SELENIUM SUPPLIED AS A MEMBER OF THE GROUP CONSISTING OF THE SELENIUM OXIDES, SELENOUS AND SELENIC ACIDS AND THE ALKALI METAL SALTS OF SAID ACIDS, AND A SOLUBLE COMPOUND OF A METAL TAKEN FROM THE CLASS CONSISTING OF CADMIUM IN AN AMOUNT FROM ABOUT 0.007 TO 7 G./L., BISMUTH IN AN AMOUNT FROM ABOUT 0.002 TO 0.05 G./L., AND SILVER IN AN AMOUNT FROM ABOUT 0.008 TO 1.62 G./L. 